Field
The described embodiments relate generally magnetic resonance (MR), more specifically to performing MR scans based on longitudinal MR histories of one or more individuals and/or medical histories of the individuals. More generally, the described embodiments relate to performing non-invasive medical imaging (such as computed tomography, ultrasound or MR imaging) based on longitudinal imaging histories of the one or more individuals and/or the medical histories of the individuals.
Related Art
Magnetic resonance or MR (which is often referred to as ‘nuclear magnetic resonance’ or NMR) is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. For example, magnetic nuclear spins may be partially aligned (or polarized) in an applied external magnetic field. These nuclear spins may precess or rotate around the direction of the external magnetic field at an angular frequency (which is sometimes referred to as the ‘Larmor frequency’) given by the product of a gyromagnetic ratio of a type of nuclei and the magnitude or strength of the external magnetic field. By applying a perturbation to the polarized nuclear spins, such as one or more radio-frequency (RF) pulses (and, more generally, electromagnetic pulses) having pulse widths corresponding to the angular frequency and at a right-angle or perpendicular to the direction of the external magnetic field, the polarization of the nuclear spins can be transiently changed. The resulting dynamic response of the nuclear spins (such as the time-varying total magnetization) can provide a wealth of information about the physical and material properties of a sample.
In medicine, MR has been widely used to non-invasively determine anatomical structure and/or the chemical composition of different types of tissue. For example, in magnetic resonance imaging (MRI), the dependence of the angular frequency of precession of nuclear spins (such as protons or the isotope 1H) on the magnitude of the external magnetic field is used to determine images of anatomical structure. In particular, by applying a non-uniform or spatially varying magnetic field to a patient, the resulting variation in the angular frequency of precession of 1H spins is typically used to spatially localize the measured dynamic response of the 1H spins to voxels, which can be used to generate images of the internal anatomy of the patient.
However, existing approaches to MRI are typically time-consuming. For example, acquiring MR images with high-spatial resolution (i.e., small voxels sizes) often involves a large number of measurements (which are sometimes referred to as ‘scans’) to be performed. Moreover, in order to achieve high-spatial resolution, a large homogenous external magnetic field is usually used during MRI. The external magnetic field is typically generated using a superconducting magnetic having a toroidal shape with a narrow bore, which can feel confining to many patients.
The combination of long scan times and the confining environment of the magnet bore can degrade the user experience during MRI. Indeed, some patients feel profoundly claustrophobic in MR scanners. In addition, long scan times reduce throughput, thereby increasing the cost of performing MM.